Ubiquitous network access has been almost realized today. From network infrastructure point of view, different networks belong to different layers (e.g., distribution layer, cellular layer, hot spot layer, personal network layer, and fixed/wired layer) that provide different levels of coverage and connectivity to users. Because the coverage of a specific network may not be available everywhere, and because different networks may be optimized for different services, it is thus desirable that user devices support multiple radio access networks on the same device platform. As the demand for wireless communication continues to increase, wireless communication devices such as cellular telephones, personal digital assistants (PDAs), smart handheld devices, laptop computers, tablet computers, etc., are increasingly being equipped with multiple radio transceivers. A multiple radio terminal (MRT) may simultaneously include a Long-Term Evolution (LTE) or LTE-Advanced (LTE-A) radio, a Wireless Local Area Network (WLAN, e.g., WiFi) access radio, a Bluetooth (BT) radio, and a Global Navigation Satellite System (GNSS) radio. In the MRT, the LTE-A radio is an Orthogonal Frequency Division Multiple Access-based (OFDMA-based) mobile broadband technology that is capable of providing global roaming services, and the WiFi radio is capable of providing huge bandwidth transmission via local access. The combination of LTE-A and WiFi radio is one of the examples of WiFi offloading, which is a common paradigm of future communications. Multiple radios co-located or coexisted in the same communication device is also referred to as in-device coexistence (IDC).
Due to spectrum regulation, different technologies may operate in overlapping or adjacent radio spectrums. For example, LTE/LTE-A TDD mode often operates at 2.3-2.4 GHz, WiFi often operates at 2.400-2.483.5 GHz, and BT often operates at 2.402-2.480 GHz. Simultaneous operation of multiple radios co-located/coexisted on the same physical device, therefore, can suffer significant degradation including significant coexistence interference (e.g., in-device interference) between them because of the overlapping or adjacent radio spectrums. Due to physical proximity and radio power leakage, when the transmission of data for a first radio transceiver overlaps with the reception of data for a second radio transceiver in time domain, the second radio transceiver reception can suffer due to interference from the transmission of the first radio transceiver. Likewise, data transmission of the second radio transceiver can interfere with data reception of the first radio transceiver.
In LTE/LTE-A systems, there are several available radio resource management (RRM) technologies to mitigate interference. Two radio resource control (RRC) states are defined for LTE UEs. One is RRC_CONNECTED state indicating that a UE is active and the other one is RRC_IDLE state indicating that a UE is idle. In one RRM scheme, when radio link failure (RLF) is declared, a user equipment (UE) may reselect to a cell in another frequency band. Another possible RRM scheme is that the UE may report measurement results (e.g., poor reference signal received power or reference signal received quality (RSRP/RSRQ) of a serving cell) to its serving base station (eNB). Furthermore, for mobility management, if a UE is active (e.g., RRC_CONNECTED state), then the network either refrains from handovering the UE to frequencies/bands with interference or handovering the UE to a cell with better signal measurement. If a UE is idle (e.g., RRC_IDLE state), then the UE avoids camping on frequency/bands with significant interference.
The current Rel-8/9 LTE RRM design, however, does not consider the effect of IDC interference. If an on-going LTE communication is severely affected by IDC, RLF will occur. However, it normally takes one second or longer for a UE to declare RLF, which results in long response time. Another issue is that, under the current RRM design, a UE may handover back to a cell in the original frequency band later, which results in ping-pong effect. In addition, Rel-8/9 backward compatibility should be considered when designing RRM that addresses the IDC interference problem.